package com.lovelilu.utils;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class MD5Utils {
         /**
     * 默认的密码字符串组合，用来将字节转换成 16 进制表示的字符,apache校验下载的文件的正确性用的就是默认的这个组合
     */
    protected static char hexDigits[] = { '0', '1', '2', '3', '4', '5', '6',
            '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f' };
 
    protected static MessageDigest messagedigest = null;
    static {
        try {
            messagedigest = MessageDigest.getInstance("MD5");
        } catch (NoSuchAlgorithmException nsaex) {
            System.err.println(MD5Utils.class.getName()
                    + "初始化失败，MessageDigest不支持MD5Util。");
            nsaex.printStackTrace();
        }
    }
     
    /**
     * 生成字符串的md5校验值
     * 
     * @param s
     * @return
     */
    public static String getMD5String(String s) {
        return getMD5String(s.getBytes());
    }
     
    /**
     * 判断字符串的md5校验码是否与一个已知的md5码相匹配
     * 
     * @param password 要校验的字符串
     * @param md5PwdStr 已知的md5校验码
     * @return
     */
    public static boolean checkPassword(String md5, String md5PwdStr) {
        return md5.equals(md5PwdStr);
    }
     
    /**
     * 生成文件的md5校验值
     * 
     * @param file
     * @return
     * @throws IOException
     */
    public static String getFileMD5String(File file) throws IOException {       
        InputStream fis;
        fis = new FileInputStream(file);
        byte[] buffer = new byte[1024];
        int numRead = 0;
        while ((numRead = fis.read(buffer)) > 0) {
            messagedigest.update(buffer, 0, numRead);
        }
        fis.close();
        return bufferToHex(messagedigest.digest());
    }
 
    public static String getMD5String(byte[] bytes) {
        messagedigest.update(bytes);
        return bufferToHex(messagedigest.digest());
    }
 
    private static String bufferToHex(byte bytes[]) {
        return bufferToHex(bytes, 0, bytes.length);
    }
 
    private static String bufferToHex(byte bytes[], int m, int n) {
        StringBuffer stringbuffer = new StringBuffer(2 * n);
        int k = m + n;
        for (int l = m; l < k; l++) {
            appendHexPair(bytes[l], stringbuffer);
        }
        return stringbuffer.toString();
    }
 
    private static void appendHexPair(byte bt, StringBuffer stringbuffer) {
        char c0 = hexDigits[(bt & 0xf0) >> 4];// 取字节中高 4 位的数字转换, >>> 为逻辑右移，将符号位一起右移,此处未发现两种符号有何不同 
        char c1 = hexDigits[bt & 0xf];// 取字节中低 4 位的数字转换 
        stringbuffer.append(c0);
        stringbuffer.append(c1);
    }
     
    /*public static void main(String[] args) throws IOException {
        long begin = System.currentTimeMillis();
 
        File file = new File("H:/12345.txt");
        String md5 = getFileMD5String(file);
        
        //文件名不同，内容相同；
        File file2 = new File("H:/12345(2).txt");
        String md52= getFileMD5String(file2);
        
        
        //文件名不同，内容不同；
        File file3 = new File("H:/12345(3).txt");
        String md53= getFileMD5String(file3);
        
      
        //测试压缩包
        File fileZip = new File("H:/1.zip");
        String md5Zip= getFileMD5String(fileZip);
        
        //测试压缩包
        File fileZip2 = new File("H:/2.zip");
        String md5Zip2= getFileMD5String(fileZip2);
           
        System.out.println("MD5:"+md5);
        System.out.println("MD5:"+md52);
        System.out.println("MD5:"+md53);
        System.out.println("MD5:"+md5Zip);
        System.out.println("MD5:"+md5Zip2);
                System.out.println("两个文件名不同，内同相同"+ checkPassword(md5, md52));
                System.out.println("文件名不同，内容不同"+ checkPassword(md5, md53));
                System.out.println("测试压缩包,内容不同"+ checkPassword(md5Zip, md5Zip2));
         
        long end = System.currentTimeMillis();
        System.out.println("md5:" + md5 + " time:" + ((end - begin) / 1000) + "s");
    }*/

}
